1. Field of the Invention
The present invention relates to a workpiece transfer apparatus for transferring workpieces in the form of a thin plate. Specifically, the invention relates to a workpiece transfer apparatus for transferring e.g. wafers in the process of manufacturing semiconductor devices.
2. Description of the Related Art
In the manufacture of semiconductor devices, a robot for transferring workpieces such as wafers is used (see JP-A-2003-188231, for example). Such a workpiece transfer apparatus transfers workpieces between a load port storing wafers and a process chamber.
FIG. 7 shows an example of workpiece transfer system including a conventional workpiece transfer apparatus. The workpiece transfer system 90 illustrated in the figure includes two load ports 91, a transfer chamber 92, a process chamber 93 and a workpiece transfer apparatus 94. The workpiece transfer apparatus 94 comprises a horizontal articulated robot having the structure described below, and is arranged in the transfer chamber 92. On one side of the transfer chamber 92, the two load ports 91 are arranged side by side adjacent to the transfer chamber 92. Each of the load ports 91 accommodates a cassette for holding a plurality of workpieces W. On a side of the transfer chamber 92 opposite from the load ports 91, the process chamber 93 is arranged adjacent to the transfer chamber 92. In the process chamber 93, treatment such as heating, working, or testing is performed with respect to the workpieces W.
FIG. 8 is a side view showing a schematic structure of the workpiece transfer apparatus 94. The workpiece transfer apparatus 94 includes a hollow stationary base 941 having a vertically extending center axis, an elevation base 942, a lower arm 943, an upper arm 944 and a hand 945. The elevation base 942 is supported by the stationary base 941 and vertically movable by the operation of an elevation mechanism, not shown. The lower arm 943 is supported at its base end on the elevation base 942 and is rotatable around the vertical axis O1 by the operation of a lower arm driving mechanism, not shown. The upper arm 944 is supported at its base end on the distal end of the lower arm 943 and is rotatable around the vertical axis O2 by the operation of an upper arm driving mechanism, not shown.
The hand 945 is supported at its base end on the distal end of the upper arm 944 and is rotatable around the vertical axis O3 by the operation of a hand driving mechanism 946. The hand driving mechanism 946 includes a hand driving motor 947 supported by the elevation base 942 and a transmission mechanism 948 for transmitting rotational output of the motor 947 to the hand 945. The transmission mechanism 948 is provided with a speed reducer 949. The speed reducer 949 is arranged directly under the base end of the hand 945, and the base end of the hand 945 is connected to the output shaft of the speed reducer 949. With this arrangement, when the motor 947 is driven, the hand 945 rotates about the vertical axis O3.
In the workpiece transfer apparatus 94 having the above-described structure, workpieces W are transferred between each of the load ports 91 and the process chamber 93 by appropriately controlling the operation of the lower arm driving mechanism, the upper arm driving mechanism and the hand driving mechanism 946.
In recent years, the size of the workpieces W, which are the object to be transferred by the workpiece transfer apparatus 94, tends to increase. For instance, in the field of semiconductor device manufacture, wafers having a diameter of 450 mm and a relatively large thickness are expected to be used instead of the wafers having a diameter of 300 mm. Such an increase in diameter and thickness of the workpieces W leads to an increase in the transfer stroke of the workpieces W in horizontal and vertical directions.
In order that the transfer efficiency of the workpieces W does not decrease even when the transfer stroke in horizontal and vertical directions is increased, the transfer speed needs to be increased. However, with the conventional workpiece transfer apparatus 94 having the above-described structure, the hand driving motor 947 is arranged in the elevation base 942 so that the power transmission path from the motor 947 to the hand 945 is relatively long. This provides limitation on the increase in the workpiece transfer speed. As another means to increase the transfer speed, increasing the size of the motor 947 or the speed reducer 949 may be considered. With the above-described conventional structure, an increase in size of the motor 947 or the speed reducer 949 results in an increase in height of the work transfer apparatus 94, whereby the height of the hand 945 increases. Such an increase in height of the hand 945 is not desirable, because the lowest position where workpieces can be transferred in the load ports 91 cannot be changed in most cases due to various limitations. Thus, with the above-described conventional structure, it is difficult to achieve transfer of relatively large workpieces W at high speed by increasing the size of the motor 947 or the speed reducer 949.
A double-hand workpiece transfer apparatus including two hands arranged in the vertical direction is also known as an apparatus for realizing more efficient workpiece transfer. Such a double-hand workpiece transfer apparatus needs to include two motors and two transmission mechanisms. With the above-described conventional structure, however, the provision of two motors and two transmission mechanisms increases the height of the workpiece transfer apparatus 94 and hence increase the height of the hand 945, so that it is difficult to adapt such an apparatus for relatively large workpieces W.